This invention relates to photoconductive semiconductors, and, more particularly, to the enhancement of photoconductivity in such semiconductors which have been prepared by the pyrolytic decomposition of one or more gaseous phase semiconductanes.
Semiconductanes are substances containing elements selected from Group IV of the Periodic Chart and thus can include germanium or tin and from Group VI, thus including selenium or tellurium. Particularly suitable semiconductanes for the production of semiconductors are the various silanes (containing silicon) and germanes (containing germanium).
There are two well established methods for producing semiconductors from semiconductanes. The first of these involves the use of a glow discharge to transform a gaseous phase semiconductane into a semiconductor. The second procedure involves the use of pyrolytic decomposition to produce the desired semiconductor.
When semiconductors have a suitable photosensitivity they can be used in photovoltaic devices such as solar cells and in devices where resistance is directly related to photoconductivity, as in the case of photodetectors.
Semiconductors produced by glow discharge are characterized by structural defects which result from the ion bombardment that is associated with the glow discharge process. As a result, it has been necessary to resort to further processing to compensate for the defects. On the other hand, amorphous silicon produced by pyrolytic decomposition, while not exhibiting the structural deficiencies associated with glow discharge, has nevertheless exhibited a lower degree of photoconductivity.
Nevertheless pyrolytically produced amorphous silicon is potentially superior to that produced by glow discharge in that the spectral response extends to longer wave lengths.
Accordingly, it is an object of the invention to enhance the photoconductivity of pyrolytically prepared semiconductors, while retaining the relatively higher long wave length quantum efficiency of such semiconductors as compared with those produced by glow discharge.
Another object of the invention is to increase the "fill factor" of pyrolytically produced solar cells. The "fill factor" of a photoresponsive solar cell is determined by the extent to which the current-voltage characteristic of the illuminated semiconductor approaches the theoretical idealized rectangular characteristic of a perfect semiconductor.
A further object of the invention is to acheive semiconductive devices, such as P-I-N photoresponsive semiconductors, in which the resultant structure exhibits enhanced photoconductivity.